Loud songs are turned down, quiet songs may be turned up on some services – IF there’s enough peak headroom.

And because the target level for some platforms is pretty loud, that’s a very significant “IF”.

YouTube and TIDAL don’t turn quieter songs up at all. And even on services that do, when there isn’t enough headroom to lift the level up without clipping, your music either won’t get turned up and will sound quieter than everything else as a result, or it may have extra peak limiting applied to get it up to the target level. Which may or may not sound good.